The present invention relates to methods for compacting soils. It aims at increasing the density of the materials in depth, so as to improve the geotechnical characteristics of the considered layer. It concerns new construction works such as construction of foundation layers for road structures, airport structures, railway structures, etc., as well as the maintenance and repair works performed under a railway, without having to proceed to the removal of the rails and of the ties.
It is known that compaction of soils or granular materials spread into a layer is usually carried out by means of compactors moving on the upper part of the layer. The compactors thus apply to the upper part of the layer an effort that will induce a pressure within the material and cause the irreversible deformations of compaction. The stresses induced within the material decrease as the depth increases and consequently the density obtained by compaction is not uniform throughout the thickness of the layer. Thus, the density distribution within the compacted material also decreases as the depth increases.
It is known in the current state of the art to choose the compactors and to define their operating characteristics according to the soil and materials and to the layer thickness in order to obtain a satisfactory density of the layer bottom, provided that the layer thickness is not too important.
Therefore, for silt or clay like soils treated with an hydraulic binder (in particular silts, more or less clayey fine sands), the maximum thickness of the compacted layer is in practice limited to 30 or 35 centimeters, because the use of the heaviest vibrating equipments would cause a surface lamination detrimental to the long term behavior/performance of the structure.
The study and calculation methods for the structures in a treated soil take of course into account the current state of the technology. It is for instance well accepted that the required density of the layer bottom shall be of 96% of the standard Proctor density (reference used in road geotechnics). It is to be noted that if a density of layer bottom equal to 100% of the standard Proctor optimum could be guaranteed, the dimensioning of the layer, with the same lifetime, could be reduced by about 20%.
It is also known that if the thickness of a foundation layer in a treated soil could be increased by 5 centimeters, with a density of the layer bottom equal to 100% of the Proctor optimum, its lifetime would be multiplied at least by 10.
Moreover, the difficulties relating to the control of this basic parameter of the compactness of the achieved layer bottom, in particular its fatigue strength, lead to take into account high safety factors.
It therefore appears that the capacity to compact the lower part of the layer and, more generally, to compact beyond the physical limits imposed by the compaction from the surface, would constitute an essential interest. It would then be possible to obtain higher compactnesses at the layer bottom and to make road layers which are thicker and in a reduced number.
It is also known that compacting the soil beneath an existing structure is not possible.
Thus, in the case of railways laid on a distribution layer made of ballast, maintenance works, without having to remove the tracks, enable the reconditioning or replacement of the ballast layer, but without the possibility to adjust and compact its base layer.
The ballast is therefore applied on a distorted support with low bearing where the rainwater stagnates and accelerates deteriorations. After two or three interventions of this type, it is necessary to reconstruct or construct a foundation layer under the ballast layer. This work requires removal of the tracks and traffic disruption over a long period.